1. Field of the Invention
The invention relates to the technical field of plant protection compositions which can be used against undesirable plant growth and which comprise, as active substances, a combination of at least two herbicides.
2. Description of Related Art
More especially, it relates to herbicidal combinations for use in rice which comprise, as active substances, a herbicide selected from the group consisting of benzoylcyclohexanediones in combination with at least one additional herbicide.
Herbicides from the abovementioned group of benzoylcyclohexanediones are known from numerous documents. Thus, for example, the herbicidal action of numerous such compounds is described in WO 00/21924. Some of the benzoylcyclohexanediones mentioned therein exhibit a satisfactory herbicidal action against harmful plants occurring in rice crops.
However, in practice, there are frequently disadvantages associated with use of the benzoylcyclohexanediones known from these documents. Thus, the herbicidal activity is not always satisfactory or, with a satisfactory herbicidal activity, undesirable damage to the rice plants is observed.
The effectiveness of herbicides depends, inter alia, on the type of herbicide used, the application rate thereof, the composition, the harmful plants to be combated each time, the climatic and soil conditions, and the like. A further criterion is the duration of the action or the rate of degradation of the herbicide. Changes in the sensitivity of harmful plants to an active substance which may occur with relatively long use or in geographically restricted areas are also to be taken into account, if appropriate. Such changes are expressed as a more or less serious loss in activity and can only to a limited extent be compensated for by higher herbicide application rates.
Because of the multitude of possible influencing factors, there is virtually no individual active substance which combines in itself the properties desired for different requirements, in particular with regard to the harmful plant species and the climatic zones. In addition, there is the constant problem of achieving the effect with an ever lower herbicide application rate. A lower application rate reduces not only the amount of an active substance required for the application but generally also reduces the amounts of formulation auxiliaries necessary. Both reduce the economic cost and improve the ecological compatibility of the herbicide treatment.
One method frequently used for improving the application profile of a herbicide consists in combining the active substance of one or more other active substances which contribute the additional properties desired. However, the combined use of several active substances not infrequently results in phenomena of physical and biological incompatibility, e.g. lack of stability of a combined formulation, decomposition of an active substance or antagonism of the active substances. On the other hand, what is desired are combinations of active substances with a favorable activity profile, high stability and the greatest possible synergistically strengthened activity which makes possible a reduction in the application rate in comparison with individual application of the active substances to be combined.
WO 02/089582 and WO 02/085118 describe herbicidal mixtures of particular benzoyl-1,3-cyclohexanediones with various herbicides. WO 02/085120 describes herbicidal mixtures of particular benzoyl-1,3-cyclohexanediones with safeners. However, in practice, there are serious disadvantages to these mixtures. Thus, their compatibility with regard to useful plants, in particular rice, is not always satisfactory and their activity with regard to harmful plants is likewise not always satisfactory.